1. Field of the Invention
This invention relates generally to cylinder locks and more particularly to a mechanism for opening and/or decoding the biddings of a key for opening a cylindrical lock.
2. Description of the Prior Art
One type of lock mechanism in wide use today is the cylinder lock. Examples of cylinder locks include pin-type tumbler locks, waffer-type tumbler locks, lever locks and combination locks. A common application for cylinder locks is in automobile doors and ignitions. In general these locks function by adjusting the elements of the lock tumblers to particular respective depths within the cylindrical lock member to enable the cylindrical lock member to rotate relative to its housing body. When the tumblers are adjusted by a key, the key must have a specific configuration to cam all the tumblers to their particular respective depths. If the key has been lost or damaged, it is necessary to provide some mechanism for causing the tumblers to move to their respective depths. Such mechanisms are generally classified as lock picking devices. Although various lock picking devices have been designed to open the cylinder locks by exerting a camming action on the tumblers, they do not enable the particular respective depths of the tumblers to be ascertained such that a new, properly configured key may be made.
To overcome the problem of providing a new properly configured key to replace a lost or damaged one, several mechanisms have been proposed as shown for example in U.S . Pat. Nos. 2,338,768 (Johnstone) and 3,827,151 (Naill). These mechanisms, called decoders, include a plurality of shims having respective cam surfaces. In the mechanism of the Johnstone patent a complicated arrangement of individual shims of various depths are required to determine the appropriate depths of pin type tumblers and corresponding biddings. In the mechanism of the Naill patent the shiftable shims, which have cam teeth with inclined sides of uniform height, are only capable of determining the depths of pin-type tumblers; and the mechanism is not capable of accurate location relative to the tumblers so that false bidding readings may occur.